Well, if that word is pronounced with a short 'a', then I guess they're pronounced the same
The two k's signify a short preceding vowel; if there only was one, it'd be pronounced with a long 'a' - which would mean 'roof' or 'ceiling'

I am from south korea. You can say '미리 감사드립니다'(mi-ri gam-sam-d-rip-ni-da) for 'Thank you in advance'. And '감사합니다'(gam-sa-hap-ni-da) for 'Thank you'. But those two sentences are pretty formal, so it's ok to say '고맙습니다'(go-map-sm-ni-da), which means 'Thanks' in every situation.